Cooling containers are used to contain a variety of products and maintain such products at a reduced temperature relative to ambient temperature for a prolonged period of time. An example of a cooling container is disclosed in E. L. Smith U.S. Pat. No. 2,526,165, which describes (in connection with FIG. 6 therein) a container having an outer bowl that surrounds an inner bowl wherein the bowls are hermetically sealed to define a chamber therebetween. A suitable refrigerant liquid such as water is disposed within the chamber. A user places the container into a household freezer for a long enough period of time to freeze the liquid. Thereafter, the user takes the container out of the freezer and may place a product, such as a perishable food item, within the container. The refrigerant liquid is capable of maintaining the food item placed in the container at a temperature below room temperature for a relatively long period of time.
Some prior art containers using a coolant or refrigerant within a cavity have included air space within the cavity to allow for expansion of the refrigerant upon freezing. Allowing for such expansion prevents such containers from rupturing. Another strategy to prevent such rupture of a cooling container is disclosed in Hilado U.S. Pat. No. 4,485,636 where the bottom of the cavity is formed by a resilient diaphragm. The diaphragm allows for expansion of the refrigerant by compressing in response to the expanding refrigerant, thereby increasing the volume of the cavity and preventing the walls of the container from breaking as a result of the expanding refrigerant.
While numerous prior art containers deal with pressure increases within a cavity due to expansion of refrigerant upon freezing, no known attempts have been made for handling pressure increases resulting from increased heat. It is possible that if a user were to place a prior art container within a microwave oven, sufficient heat and pressure would develop within the sealed cavity to rupture the walls of the container.